This invention relates to systems and methods of rapid prototyping and production (or called additive manufacturing or 3D printing). Especially, this invention relates to fabricating 3D prototypes, articles, components and molds at improved surface finish and increased speed.
Existing major rapid prototyping (also known as additive manufacturing or 3D printing) techniques include methods such as SLM (Selective Laser Melting) for making metal parts (for examples, EOS M400, referring to http://www.eos.info/systems_solutions/metal/systems_equipment/eos_m_400, 3D Systems SPro 250, see http://production3dprinters.com/sites/production3dprinters.com/files/downloads/sPro-125-250-SLM-Direct-Metal.pdf, or Renishaw AM250, referring to http://www.renishaw.com/en/am250-laser-melting-machine--15253)), and SLA ((Stereolithography) (for example, 3D Systems ProJet HD 7000, referring to http://printin3d.com/sites/printin3d.com/files/downloads/ProJet-6000-7000-USEN.pdf), FDM (Fused Deposition Modeling) (e.g. Stratasys FDM 900m, referring to http://www.fortus.com/Products/Fortus-900mc.aspx) and 3DP (3D Printing) (jetting binders to powder bed layer-by-layer) for making plastic parts.
In general, these existing rapid prototyping methods apply a layer-by-layer construction methodology. Materials are dispensed in horizontal layers and within each layer joined by point scanning. Material build-up by horizontal layers, regardless of the 3D shape to be built, creates inevitable layered (stairs-like) surface feature, resulting in poor surface finish. Material joining by point scanning is basically “scanning a 3D body by one tiny point”, resulting in slow build-up rate. Combined operation of layer dispensing and point-scanning joining slows down the process further. FIG. 1 illustrates an example 3D part. FIG. 2 illustrates the fabrication of this example 3D part by the existing methodology. FIG. 2(a) shows the blade portion and FIG. 2(b) shows the cross-sectional view. Dotted lines 201 indicate the grid structure of horizontal layers and solid curves 203 indicate trajectories of point scanning. Stairs-like surface features at 214 and 212 are inevitable.
When using the SLM technique to make a mold for plastic injection molding, the surface finish can be about 40 um Ra and a machining tolerance of 200˜500 um is generally required, which makes post machining cost significant. There are studies on post polishing using laser beams. (Referring to Lamikiz et al., “Laser polishing of parts built up by selective laser sintering”; International Journal of Machine Tools & Manufacture 47 (2007) 2040-2050). In order to improve forming speed, a so called “skin-core strategy” was developed, which uses a laser of small focal spot to scan edges of patterns in each layer and a larger focal spot to scan the interior. (Referring to (1) K. Wissenbach, “Fantasia Project Shows Selective Laser Melting Can Produce Complex Components Quickly and Cost Effectively”, http://www.ineffableisland.com/2010/05/fantasia-project-shows-selective-laser.html?showComment=1318241730096; (2) C. Hinke, “Direct, Mould-less Production Systems”, http://www.production-research.de/_C12577F20052BDC7.nsf/html/de_040d66b2c812b739c1257829005207de.html). But these methods also increase equipment costs.
In the FDM technique, U.S. Pat. No. 5,121,329, which is incorporated herein for this current application by reference, describes methods of moving a material dispensing head along curved trajectories to produce curved surfaces or frames and of dispensing materials of variable thickness by changing material feed rate (referring to FIG. 10 and FIG. 12 of that patent). However, because the FDM method uses a fixed orifice size to dispense material, the effect of speed Increasing is likely to be limited. In another FDM related technique, U.S. Pat. No. 8,221,669, which is incorporated herein for this current application by reference, describes the use of ribbon (non-cylindrical) filament as material, in contrast to the cylindrical filament used in most current commercial systems, in order to reduce the so called “response time”, that is, the delay time from the start or stop of the feeding mechanism to the actual flow rate change at the tip of the extrusion tip of the liquefier. But it should be noted that faster material deposition is not the purpose nor mentioned in this patent.
There are other methods developed or under development for making metal objects.
For example, applying the FDM technique to make metal parts has been attempted. U.S. Pat. No. 7,942,987, which is incorporated herein for this current application by reference, describes a method of heating a metal alloy to a temperature between a solidus temperature and a liquidus temperature to obtain a semi-solid metal alloy with enough viscosity so that it can be extruded. However, the “point scanning” and “layer by layer” issues are not addressed in this approach.
Another approach is called Laser Deposition Technology (LDT) or Laser Engineered Net Shape (LENS). Metal powder is injected into a focused beam of a high-power laser under tightly controlled atmospheric conditions. The focused laser beam melts the surface of the target material and generates a small molten pool of base material. Powder delivered into this same spot is absorbed into the melt pool, thus generating a deposit. By moving the laser beam and the deposition relative to the target material, 3D shapes can be built up. A description of the process can be found from http://www.rpm-innovations.com/laser_deposition_technology and related technical details can be seen in U.S. Pat. Nos. 4,323,756 and 5,043,548, which are incorporated herein by reference. A very similar method, except using wire metal instead of powder, was described in U.S. Pat. No. 5,578,227, which is incorporated herein by reference. In general, these approaches are basically still a “point scanning” based approach. Further, surfaces of built-up parts are usually rough.